Electrode foil and organic device

ABSTRACT

There are provided an electrode foil which has both the functions of a supporting base material and a reflective electrode and also has a superior thermal conductivity and heat resistance; and an organic device using the same. The electrode foil comprises a metal foil; a diffusion prevention layer for preventing diffusion of metal derived from the metal foil, the diffusion prevention layer being provided directly on the metal foil; and a reflective layer provided directly on the diffusion prevention layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2010-211189 filed on Sep. 21, 2010, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode foil using a metal foil, and to an organic device using the electrode foil, such as an organic EL element, an organic EL lighting, an organic solar cell or the like.

2. Description of Related Art

In recent years, organic EL lighting has been drawing attention as an eco-friendly green device. Features of the organic EL lighting include: 1) a low power consumption as compared with an incandescent lamp; 2) a thin profile and light weight; and 3) a flexibility. At the moment, the organic EL lightings are being developed so as to attain the above features of 2) and 3). In this respect, glass substrates that have been conventionally used in flat panel displays (FPD) and the like are unable to attain the above features of 2) and 3).

In view of this, there are researches being conducted on a substrate as a support (hereinafter, “supporting base material”) for organic EL lighting, proposing an ultra-thin glass, a resin film, a metal foil or the like as a possible supporting base material. The ultra-thin glass is superior in heat resistance, barrier performance and optical transparency and has good flexibility, but is somewhat inferior in handling and has low thermal conductivity and high material cost. Further, the resin film is superior in handling and flexibility and has low material cost and good optical transparency, but is inferior in heat resistance and barrier performance and has low thermal conductivity.

In contrast, apart from the absence of optical transparency, the metal foil has excellent features such that it is superior in heat resistance, barrier performance, handling, and thermal conductivity and also has good flexibility and low material cost. In particular, a typical flexible glass or film has an extremely low thermal conductivity of 1 W/m° C. or lower, while a copper foil has an extremely high thermal conductivity of around 280 W/m° C. However, in order to use the metal foil as a supporting base material for flexible electronic devices, the surface of the metal foil needs to be covered with an insulating film.

For instance, Patent Literature 1 (JP2007-536697A) discloses an organic light-emitting device comprising a lower electrode layer, an organic layer, and an upper electrode layer on a flexible substrate, describing that a metal foil that may be covered with an insulating film can be used as the flexible substrate.

Patent Literature 2 (JP2008-142970A) discloses an insulator-coated metal foil for flexible electronic devices, which comprises a stainless steel foil having a surface roughness Ra of from 30 nm to 500 nm. The metal foil, of which the surface is coated with the insulator film, is used as a supporting base material for forming thereon an electronic device, such as thin film transistor (TFT).

Patent Literature 3 (JP2001-270036A) discloses a flexible metal foil laminate comprising a metal foil having a surface roughness Ra of about 0.2 μm or less and a heat-adhesive polyimide coating laminated on the surface the metal foil.

Patent Literature 4 (JP2007-217787A) discloses an electrolytic copper foil having a surface roughness (Rzjis) of less than 1.0 μm on the deposition side thereof so as to attain a low profile on the surface to be bonded to an insulator-layer constituent material. However, the surface roughness (Rzjis) disclosed in this literature is 0.27 μm at best.

CITATION LIST Patent Literature

-   [Patent Literature 1] JP2007-536697A -   [Patent Literature 2] JP2008-142970A -   [Patent Literature 3] JP2001-270036A -   [Patent Literature 4] JP2007-217787A

SUMMARY OF THE INVENTION

The inventors have currently found that providing a reflective layer on a metal foil enables attainment of an electrode foil useful for flexible organic devices, which has both the functions of a supporting base material and a reflective electrode and also has a superior thermal conductivity. Moreover, interposing a diffusion prevention layer, which prevents diffusion of metal derived from the metal foil, between the reflective layer and the metal foil enables an improvement in the heat resistance of the electrode foils.

It is thus an object of the present invention to provide an electrode foil useful for flexible organic devices, which has both the functions of a supporting base material and a reflective electrode and also has a superior thermal conductivity and heat resistance.

According to an aspect of the present invention, there is provided an electrode foil comprising:

-   -   a metal foil;     -   a diffusion prevention layer for preventing diffusion of metal         derived from the metal foil, the diffusion prevention layer         being provided directly on the metal foil; and     -   a reflective layer provided directly on the diffusion prevention         layer.

According to another aspect of the present invention, there is provided an organic device which is an organic EL element and/or an organic solar cell, the organic device comprising:

-   -   the above electrode foil;     -   an organic semiconductor layer comprising an organic EL layer         and/or an organic solar cell active layer, the organic         semiconductor layer being provided directly on an outermost         surface on or to the side of the reflective layer of the         electrode foil; and     -   a transparent or translucent counter electrode provided on the         organic semiconductor layer.

According to still another aspect of the present invention, there is provided an organic EL lighting comprising the above organic device as an organic EL element.

BRIEF DESCRIPTON OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an example of the electrode foil according to the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a layer structure of an organic EL element in which the electrode foil according to the present invention is used as an anode.

FIG. 3 is a schematic cross-sectional view illustrating an example of a top-emission type organic EL lighting according to the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a layer structure of an organic EL element in which the electrode foil according to the present invention is used as a cathode.

FIG. 5 is a photograph showing a light-emitting appearance of an organic EL element prepared in Example 4.

FIG. 6 is a graph showing the voltage dependence of brightness measured in Examples 4 and 5.

FIG. 7 is a graph showing the voltage dependence of current density measured in Examples 4 and 5.

FIG. 8 is a graph showing the voltage dependence of brightness measured in Example 5.

FIG. 9A is a microphotograph of a cross-section of the Cu/C/Al-alloy laminate in the electrode foil with the diffusion prevention layer (Cu/C/Al-alloy/C) prepared in Example 6 as observed by TEM.

FIG. 9B is a spectrum obtained by performing EDX analysis on point B on a cross-section of the Al-alloy layer shown in FIG. 9A.

FIG. 9C is a spectrum obtained by performing EDX analysis on point C on a cross-section of the copper foil shown in FIG. 9A.

FIG. 10A is a microphotograph of a cross-section of the Cu/Cr—Ti/Al-alloy laminate in the electrode foil with the diffusion prevention layer (Cu/Cr—Ti/Al-alloy/C) prepared in Example 7 as observed by TEM.

FIG. 10B is a spectrum obtained by performing EDX analysis on point B on a cross-section of the Al-alloy layer shown in FIG. 10A.

FIG. 10C is a spectrum obtained by performing EDX analysis on point C on a cross-section of the copper foil shown in FIG. 10A.

FIG. 11A is a photograph of a cross-section of the Cu/Al-alloy laminate in the electrode foil with no diffusion prevention layer (Cu/Al-alloy/C) prepared in Example 8.

FIG. 11B is a spectrum obtained by performing EDX analysis on point B on a cross-section of the Al-alloy layer shown in FIG. 11A.

FIG. 11C is a spectrum obtained by performing EDX analysis on point C on a cross-section of the copper foil shown in FIG. 11A.

DETAILED DESCRIPTION OF THE INVFNTION

Electrode Foil

FIG. 1 shows a schematic cross-sectional view of an example of the electrode foil according to the present invention. The electrode foil 10 shown in FIG. 1 comprises a metal foil 12; a diffusion prevention layer 13 provided directly on the metal foil; a reflective layer 14 provided directly on the diffusion prevention layer; and optionally a buffer layer 15 provided directly on the reflective layer. Although the electrode foil 10 has a four-layer structure composed of the metal foil 12, the diffusion prevention layer 13, the reflective layer 14 and the buffer layer 15, the electrode foil of the present invention is not limited thereto but may be a three-layer structure composed of the metal foil 12, the diffusion prevention layer 13 and the reflective layer 14. While formation of a reflective layer on a metal electrode layer is generally conducted in top-emission type organic EL elements, it has been believed that the metal electrode layer needs to be formed on a supporting base material such as an insulator substrate. Indeed, to the best of the inventors' knowledge, no attempt has been ever made to form a reflective layer on a metal foil that can be handled solely in itself and then to use this metal foil as an anode or a cathode of an organic EL element. In the present invention, using the metal foil 12 not only as a supporting base material but also as an electrode and providing a reflective layer 14 thereabove via the diffusion prevention layer 13 make it possible to provide an unprecedented electrode foil which combines three functions as a supporting base material, an electrode and a reflective layer. The electrode foil of the present invention thus makes it possible to dispense with a supporting base material and a reflective layer that have been needed in conventional top-emission type flexible light-emitting devices. Accordingly, the electrode foil of the present invention is free from an insulator layer at least on or to the side of the reflective layer, and preferably is free from an insulator layer at any position.

The metal foil 12 is not particularly limited as long as the metal foil is a foil-like metallic material that has a strength required for a supporting base material and electrical properties required for an electrode. A preferred metal foil is a nonmagnetic metal foil from the view point of preventing magnetic adherence of particles produced on machining. Examples of the nonmagnetic metal preferably include copper, aluminum, nonmagnetic stainless steel, titanium, tantalum, and molybdenum, and more preferably copper, aluminum, and nonmagnetic stainless steel. The most preferable metal foil is copper foil. Copper foil is relatively inexpensive as well as excellent in strength, flexibility, and electrical properties.

At least one of the outermost surfaces of the electrode foil 10 is preferably an ultra-smooth surface having an arithmetic average roughness Ra of 10.0 nm or less, more preferably 7.0 nm or less, further preferably 5.0 nm or less, most preferably 3.0 nm or less. The lower limit of the arithmetic average roughness Ra is not particularly limited but may be 0 (zero). However, considering efficiency of surface smoothing treatment, 0.5 nm may be considered the lower limit. The arithmetic average roughness Ra may be measured in accordance with JIS B 0601-2001 by using a commercially available surface roughness meter.

The expression “at least one of the outermost surfaces of the electrode foil 10” denotes the surface 14 a of the reflective layer 14 in the case of the three-layer structure or the surface 15 a of the buffer layer 15 in the case of the four-layer structure. The aforementioned arithmetic average roughness Ra of the surface 14 a of the reflective layer 14 in the case of the three-layer structure may be attained by providing the surface 13 a of the diffusion prevention layer 13 and the surface 12 a of the underlying metal foil 12 for the reflective layer 14 to be formed thereon with arithmetic average roughnesses Ra in a range similar to those mentioned above, namely, 10.0 nm or less, preferably 6.0 nm or less, more preferably 3.0 nm or less; and forming a reflective layer 14 thereon. In the case of the four-layer structure, the aforementioned arithmetic average roughness Ra of surface 15 a of buffer layer 15 may be attained by forming a buffer layer 15 on the reflective layer 14 provided with an arithmetic average roughness Ra of 10.0 nm or less, preferably 6.5 nm or less, more preferably 4.0 nm or less as described above. The surface 15 a of the buffer layer 15 thus formed has an arithmetic average roughness Ra of 10.0 nm or less, preferably 7.0 nm or less, more preferably 5.0 nm or less. As described above, it is preferred that the surface of a layer or foil underneath the outermost surface be provided with an arithmetic average roughness Ra equivalent to or somewhat smaller than an arithmetic average roughness Ra to be provided on the outermost surface. The arithmetic average roughness Ra of the metal foil surface not constituting the outermost surface due to the lamination state may be evaluated by creating a cross section from the metal foil surface by FIB (Focused Ion Beam) processing; and observing the cross section with a transmission electron microscope (TEM). The arithmetic average roughness Ra of the reflective layer surface not constituting the outermost surface due to the lamination state may be evaluated in the same way.

As far as the present inventors are aware, a metal foil (particularly, a copper foil) having the aforementioned ultra-smooth surface has not been industrially produced to date, nor has there been any attempt to apply the metal foil to an electrode itself of flexible electronic devices. A copper foil with a smoothed surface is commercially available, but such a surface smoothness level of the copper foil is not sufficient for organic EL element electrodes in that incorporating the foil to prepare an organic EL element may result in short circuit due to the unevenness and thus fails to provide light emission.

In contrast, when the arithmetic average roughness Ra of the ultra-smooth surface 12 a of the metal foil 12 is extremely small to such an extent of preferably 10.0 nm or less, more preferably 6.0 nm or less, further preferably 3.0 nm or less, short circuit that may occur between the foil and a counter electrode or the like can be effectively prevented, even if the foil is used as an organic EL element electrode. Such an ultra-smooth surface may be attained by polishing the metal foil with CMP (Chemical Mechanical Polishing) treatment. CMP treatment may be performed by using a known polishing liquid and a known polishing pad under known conditions. A preferable polishing liquid may comprises one or more of polishing granules selected from ceria, silica, alumina, zirconia, and others in an amount of from about 0.5 to about 2 wt %; an oxidizing agent such as benzotriazole (BTA); and/or an organic complex forming agent such as quinaldic acid, quinolinic acid, and nicotinic acid; a surfactant such as a cationic surfactant and an anionic surfactant; and optionally an anticorrosive agent. A preferable polishing pad is a pad made of urethane. The polishing conditions are not particularly limited as pad rotation speed, work load, coating flow rate of polishing liquid may be adequately regulated. It is preferable that the rotation speed be regulated in the range of from 20 rpm to 1,000 rpm, that the work load be regulated in the range of from 100 gf/cm² to 500 gf/cm², and that a coating flow rate of the polishing liquid be regulated in the range of from 20 cc/min to 200 cc/min.

The ultra-smooth surface 12 a may be attained by polishing metal foil 12 using electrolytic polishing, buff polishing, chemical polishing, or a combination thereof. Chemical polishing is not particularly limited as it may be performed by adequately adjusting a chemical polishing solution, the temperature of the chemical polishing solution, dipping time in the chemical polishing solution, and the like. For instance, chemical polishing of copper foil may be performed by using a mixture of 2-aminoethanol and ammonium chloride. The temperature of the chemical polishing solution is preferably room temperature, while dipping method (Dip process) is preferably used. Further, dipping time in the chemical polishing solution is preferred to be from 10 to 120 seconds, more preferably from 30 to 90 seconds since long dipping time tends to result in degradation of smoothness. The metal foil after chemical polishing is preferred to be cleansed with running water. This smoothing treatment can smooth the surface having an arithmetic average roughness Ra of about 12 nm to have an Ra of 10.0 nm or less.

The ultra-smooth surface 12 a may also be attained by a technique such as a method of polishing the surface of the metal foil 12 by blasting or a method of melting the surface of the metal foil 12 by laser, resistance heating, lamp heating or the like and then rapidly cooling the surface of the metal foil 12. In the case of using, as the metal foil 12, a platable foil made of a metal such as copper, nickel, and chromium, the ultra-smooth surface may also be attained by using a transfer method. The transfer method may be conducted in accordance with known techniques and known conditions. For instance, the surface of an electrode plate such as SUS and titanium is smoothed by electrolytic polishing and buff polishing so as to be provided with an arithmetic average roughness Ra of 10.0 nm or less. The surface of the electrode plate thus smoothed was plated with the material of metal foil 12, which is peeled off from the electrode plate when a desired thickness is attained. In this way, by transferring the smoothness of the electrode plate surface to the peeled face of the metal foil 12, an ultra-smooth surface can be attained.

The thickness of the metal foil 12 is not particularly limited as long as the metal foil does not lose flexibility and can be handled solely in itself, but may be in the range of from 1 μm to 250 μm, preferably from 25 μm to 250 μm, and more preferably from 35 μm to 150 μm. With such thickness, cutting may be performed easily by using a commercially available cutting machine. In addition, unlike glass substrates, the metal foil 12 has no problems such as crack, chip or the like, and also has an advantage of not easily producing particles upon cutting. The metal foil 12 may be formed in various shapes other than tetragon, such as circle, triangle, and polygon, and can also be cut-and-pasted to prepare a light emitting body in a three-dimensional shape such as a cubic shape or a ball shape since the metal foil is capable of being cut or welded. In this case, it is preferred that a light emitting layer be not formed at a cutting or welding portion of the metal foil 12.

The ultra-smooth surface 12 a is preferably cleansed with an alkaline solution. A known alkaline solution such as an ammonia-containing solution, a sodium hydroxide solution, and a potassium hydroxide solution may be used as the alkaline solution. The alkaline solution is preferably an ammonia-containing solution, more preferably an organic alkaline solution containing ammonia, further preferably a tetramethylammonium hydroxide (TMAH) solution. Preferable concentration of the TMAH solution is from 0.1 wt % to 3.0 wt %. An example of washing described above includes performing cleansing at 23° C. for one minute with use of a 0.4% TMAH solution. A similar cleansing effect can also be attained by performing UV (Ultra Violet) treatment in combination with or in place of the alkaline solution. In addition, in the case of copper foil and the like, it is possible to remove oxides formed on the copper surface by using an acidic cleansing solution such as dilute sulfuric acid. An example of acid cleansing includes performing cleansing for 30 seconds with dilute sulfuric acid.

Prior to the formation of the diffusion prevention layer 13, it is preferred that particles on the ultra-smooth surface 12 a be removed. Examples of an effective method for removing the particles include a sonic washing method using ultra-pure water and a dry-ice blasting method. The dry-ice blasting method is more effective. Dry-ice blasting method is a method of ejecting carbon dioxide gas compressed at high pressure through a fine nozzle and thereby blowing carbon dioxide solidified at low temperature against the ultra-smooth surface 12 a to remove the particles. Unlike wet process, this dry-ice blasting method can dispense with drying process, and also has an advantage of being able to remove organic substances. The dry-ice blasting method may be performed by using a commercially available apparatus such as a dry-ice snow system (manufactured by AIR WATER INC.).

The diffusion prevention layer 13 is directly provided on the ultra-smooth surface of the metal foil 12 a. Any films having known compositions and structures can be used as the diffusion prevention layer 13 as long as it has a function of preventing diffusion of metal derived from the metal foil. As a result, even when the electrode foil is exposed to a considerably high temperature, thermal migration that may occur from the interface between the copper foil and the aluminum-containing reflective layer can be effectively suppressed, making it possible to prevent deterioration of the surface smoothness and optical reflectivity caused by the thermal migration. That is, heat resistance of the electrode foil can be improved. Therefore, the above embodiment is particularly effective in heat treatment which is performed at a temperature of 200° C. or higher, preferably 230° C. or higher, and more preferably 250° C. or higher after a hole injection layer is coated. The diffusion prevention layer 13 may be a layer structure composed of two or more layers.

Preferable materials for constituting the diffusion prevention layer 13 include (i) high-melting metals such as Mo, Ti, Ta, Cr and W, alloys and nitrides thereof; (ii) transition metals such as Ni, Fe, Co and alloys thereof; and (iii) an conductive amorphous carbon, an conductive oxide, a magnesium alloy, and a fluoride, which can also be used for the buffer layer. Therefore, examples of the diffusion prevention layer include layers comprising at least one of Mo, Ti, Ta, Cr, W, Ni, Fe, Co, C, Zn, Li, Y, indium oxide, tin oxide, zinc oxide, molybdenum oxide, gallium oxide, vanadium oxide, tungsten oxide, ruthenium oxide, aluminum oxide, titanium oxide, titanium nitride, chromium nitride, tantalum nitride, NIP, Ni—Zn, LiF, MgF₂, CaF₃, NaAlF₆, and NaF₆. In addition, these compounds are not limited to those having stoichiometric compositions. For example, a substance such as indium oxide (In₂O₃) partially devoid of oxygen can also be used as the diffusion prevention layer. This makes it possible to effectively prevent thermal migration, while bringing the metal foil 12 into close contact with the reflective layer 14 electrically and mechanically. Formation of the diffusion layer may be done in accordance with various known methods such as sputtering method, vacuum deposition method, electroplating method, non-electrolytic plating method and the like. The thickness of the diffusion prevention layer 13 is not limited as long as there can be achieved the effect of preventing diffusion of metal as required for the diffusion prevention layer, but is preferred to be 1 nm or more, more preferably 3 nm or more, further preferably 5 nm or more. In addition, in terms of retaining the surface smoothness of the electrode foil, the thickness of the diffusion prevention layer 13 is preferred to be 200 nm or less, more preferably 100 nm or less.

The reflective layer 14 is provided directly on the ultra-smooth surface of the diffusion prevention layer 13 a. The reflective layer 14 is preferred to be composed of at least one selected from the group consisting of aluminum, aluminum alloys, silver, and silver alloys. These materials are suitable for a reflective layer due to a high optical reflectivity and also excellent in smoothness when being formed into thin films. In particular, aluminum and aluminum alloys are preferable, because they are inexpensive materials. A wide variety of aluminum alloys and silver alloys can be adopted having conventional alloy compositions for use as an anode or a cathode of a display device such as an organic EL element. Preferred examples of the aluminum alloy compositions include Al—Ni; Al—Cu; Al—Ag; Al—Ce; Al—Zn; Al—B; Al—Ta; Al—Nd; Al—Si; Al—La; Al—Co; Al—Ge; Al—Fe; Al—Li; Al—Mg; and Al—Mn. Any element that can constitute these alloys may be combined arbitrarily, depending on required performances. Preferred examples of the silver alloy compositions include Ag—Pd; Ag—Cu; Ag—Al; Ag—Zn; Ag—Mg; Ag—Mn; Ag—Cr; Ag—Ti; Ag—Ta; Ag—Co; Ag—Si; Ag—Ge; Ag—Li; Ag—B; Ag—Pt; Ag—Fe; Ag—Nd; Ag—La; and Ag—Ce. Any element that can constitute these alloys may be combined arbitrarily, depending on required performances. The thickness of the reflective layer 13 is not particularly limited, but is preferably from 30 nm to 500 nm, more preferably from 50 nm to 300 nm, and further preferably from 100 nm to 250 nm.

The surface 14 a of the reflective layer 14 has an arithmetic average roughness Ra of preferably 10.0 nm or less, more preferably 6.5 nm or less, further preferably 4.0 nm or less. As described above, since the reflective layer is formed on the ultra-smooth surface of the metal foil in the present invention, it is possible to provide a small arithmetic average roughness Ra even on the surface of the reflective layer and thus to attain a higher smoothness. This enables reduction in risk of short circuit between the organic EL layers, which is caused by occurrence of excessive unevenness. In addition, since there is no need to thickly form a hole injection layer and a hole transport layer or an electron injection layer and an electron transport layer for eliminating the effect of unevenness of the reflective layer surface, these layers and an organic EL layer that includes these layers may be made thinner than conventional thicknesses. As a result, it is possible to reduce the usage of extremely expensive organic raw materials so as to lower production cost as well as to make the organic EL layer thinner so as to improve light-emitting efficiency.

It is preferred that the buffer layer 15 be provided directly on the reflective layer 14. The buffer layer 15 is not particularly limited as long as it makes contact with an organic EL layer in an organic EL element to improve hole injection efficiency or electron injection efficiency as well as to provide a desired work function. Nonetheless, the buffer layer in the present invention is preferably transparent or translucent from the viewpoint of enabling the metal foil to function as a reflective layer.

The buffer layer 15 is preferably at least one selected from the group consisting of an conductive amorphous carbon film, an conductive oxide film, a magnesium alloy film, and a fluoride film, and may be selected as needed depending on applications such as an anode or a cathode and required performances.

As the conductive amorphous carbon film, various kinds of amorphous carbon films provided with electrical conductivity by regulating hydrogen concentration or impurity concentration may be used. Formation of the conductive amorphous carbon film is preferred to be conducted by sputtering. A carbon target subjected to purification treatment is desired to be used for the sputtering. In addition, porous carbon impregnated with B, Si, Al and/or Cu may be used. When the conductive amorphous carbon film is used as the buffer layer, any of an aluminum film, an aluminum alloy film, a silver film, and a silver alloy film may be suitably used for the reflective layer, while aluminum alloys are preferable in consideration of smoothness and material cost.

A preferable conductive amorphous carbon film is composed of an conductive amorphous carbon having a hydrogen concentration of 15 at % or less. The hydrogen concentration is more preferably 12 at % or less and further preferably 5 at % or less. Although the lower limit of the hydrogen concentration is not particularly limited but may be 0 (zero), a typical lower limit may be 3 at % in consideration of unavoidable contamination with hydrogen from film forming environment upon sputtering. The hydrogen concentration in the buffer layer may be measured by various known methods, among which HFS (Hydrogen Forward Scattering) is preferred. The hydrogen concentration in the conductive amorphous carbon film is defined herein as a hydrogen concentration obtained by measuring the amounts of carbon and hydrogen by HFS or the like and assuming the total amount of these atoms as 100 at %. Extremely lowering the hydrogen concentration in this way makes it possible to avoid decrease in electrical conductivity or development of insulation properties, which are caused by the carbon atoms constituting the buffer layer being terminated with hydrogen, and thus to provide the buffer layer with a high electrical conductivity required for an electrode. Therefore, it is preferable that the conductive amorphous carbon be not substantially doped with impurities other than carbon and hydrogen. The phrase “not substantially doped” means that impurities are not intentionally added for the purpose of providing a certain function, allowing impurities unavoidably incorporated from film forming environment or the like during sputtering. In view of this, the conductive amorphous carbon in the present invention preferably has an oxygen concentration of from 0 wtppm to 300 wtppm, a halogen element concentration of from 0 wtppm to 1,000 wtppm, and a nitrogen concentration of from 0 wtppm to 500 wtppm. The thickness of the buffer layer 14 is not particularly limited, but preferably from 3 nm to 30 nm, more preferably from 3 nm to 15 nm, and further preferably from 5 nm to 10 nm.

A preferable conductive oxide film may be composed of one or more selected from the group consisting of InO_(N), SnO_(x), ZnO_(x), MoO_(x), GaO_(x), VO_(x), WO_(x), RuO_(x), AlO_(x), TiO_(x), and GeO_(x). Typical examples thereof include ITO (indium tin oxide) and IZO (indium zinc oxide). The conductive oxide film may be formed by using a known technique such as sputtering and vacuum deposition, preferably DC magnetron sputtering. The target material used for sputtering may be prepared by hot pressing or cold pressing, so that the oxides described above may be combined together as needed to attain desired characteristics. When the conductive oxide film is used as the buffer layer, Al—Ni alloys, Ag, and Ag alloy are particularly suitable for the reflective layer.

A preferable magnesium alloy film may be composed of an alloy comprising Mg and one or more additive selected from the group consisting of Ag, Al, Zn, Li, Y, and Ca. The magnesium alloy film may be formed by using a known technique such as sputtering method or vacuum deposition method, preferably vacuum deposition method.

A preferable fluoride film may be composed of one or more selected from the group consisting of LiF, MgF₂, CaF₂, AlF₃, Na₃AlF₆, and NaF₆. The fluoride film may be formed by using a known technique such as sputtering method or vacuum deposition method, preferably vacuum deposition method.

The surface 15 a of the buffer layer 15 has an arithmetic average roughness Ra of 10.0 nm or less, preferably 7.0 nm or less, more preferably 5.0 nm or less. As described above, the buffer layer is formed on the ultra-smooth surface of the reflective layer of which the ultra-smoothness arises from the ultra-smooth metal foil, so that the arithmetic average roughness Ra may be reduced also on the surface of the buffer layer to realize a high smoothness. This makes it possible to reduce the risk of short circuit in the organic EL layer, which arises from generation of excess unevenness. In addition, a hole injection layer and a hole transport layer or an electron injection layer and an electron transport layer are not needed to be formed thick so as to eliminate the influence of unevenness of the buffer layer surface. Therefore, these layers and an organic EL layer that includes these layers may be made thinner than usual. As a result, the amount of extremely expensive organic raw materials to be used is reduced to lower production cost, while the organic EL layer can be thinned to increase light-emitting efficiency.

An oxide film (not shown in figures) may exist between the reflective layer 14 and the buffer layer 15. The oxide film may be formed typically by allowing the anode layer to be inevitably oxidized by atmospheric oxygen. The oxide film is preferred to be as thin as possible, with a thickness being preferably 3.0 nm or less, more preferably 1.5 nm or less. The oxide film may be removed by etching or the like.

The electrode foil of the present invention has a thickness of preferably from 1 μm to 300 μm, more preferably from 25 μm to 250 μm, further preferably from 35 μm to 150 μm, most preferably from 40 μm to 100 μm.

According to a preferred embodiment of the present invention, the surface 12 b of the metal foil 12 opposite to the reflective layer 14 may be roughened to a ten-point average roughness Rz of 1.0 μm or more, more preferably 2.0 μm or more, and further preferably 5.0 μm or more. The ten-point average roughness Rz may be measured in accordance with JIS B 0601-1994 with a commercially available roughness meter available. The surface may be roughened preferably by using a known technique such as dry-ice blasting, sand blasting, wet etching, dry etching, or the like. The unevenness provided on the roughened surface can improve heat discharge characteristics.

The electrode foil of the present invention is metal-foil based, so that the electrode foil can be produced efficiently, for example, by roll-to-roll process without particularly necessitating a supporting base material.

The electrode foil of the present invention may be used preferably as an anode or a cathode for various kinds of flexible organic devices (particularly, flexible light-emitting or power generating devices), thereby functioning as a reflective electrode. Examples of such flexible organic devices include organic EL elements; organic EL lighting; organic EL displays; electronic paper; thin-film solar cells; liquid crystal displays; inorganic EL elements; inorganic EL displays; LED lighting; and LED displays. Preferred are organic EL elements, organic EL lighting, organic EL displays, organic solar cells, and dye-sensitized solar cells. Organic EL lighting is more preferable in that high brightness is attained in an ultra-thin form. In addition, since many of characteristics required for electrode materials of organic solar cells are in common with those required for organic EL elements, the electrode foil of the present invention may be preferably used as an anode or a cathode of organic solar cells. Namely, appropriate selection of the kind of an organic semiconductor layer to be laminated on the electrode foil of the present invention in accordance with known techniques makes it possible to construct an organic device in any form of an organic EL element and an organic solar cell. It is also possible to form a light-emitting element and a power generating element simultaneously on the same electrode, and thereby to fabricate a composite device that has both functions of an organic EL element and an organic solar cell. Furthermore, the electrode foil of the present invention may be used not only as an electrode of an organic EL element but also as an LED mounting board. In particular, the electrode foil of the present invention may be preferably used as an anode or a cathode of LED lighting in that LED elements can be mounted in a closely packed manner.

Organic EL elements and Organic EL Lighting

A top-emission type organic EL element and an organic EL lighting may be constructed by using the electrode foil of the present invention as a reflective electrode.

FIG. 2 shows an example of a layer structure of a top-emission type organic EL element that uses the electrode foil of the present invention as an anode. The organic EL element shown in FIG. 2 comprises an anodic electrode foil 20 comprising a metal foil 22, a diffusion prevention layer 23, a reflective layer 24 and a buffer layer 25; an organic EL layer 26 provided directly on the buffer layer 25; and a cathode 28 as a counter electrode provided directly on the organic EL layer 26. It is preferred that the buffer layer 25 be composed of a conductive amorphous carbon film or a conductive oxide film so as to be suitable as an anode.

The organic EL layer 26 may employ various known EL layer structures used for organic EL elements and may comprise optionally a hole injection layer and/or a hole transport layer, a light-emitting layer, and optionally an electron transport layer and/or an electron injection layer in this order in the direction from the anodic electrode foil 20 to the cathode 28. Any various known structures or compositions may be appropriately employed for each of the hole injection layer, the hole transport layer, the light-emitting layer, the electron transport layer, and the electron injection layer, without any particular limitation.

As described above, an organic solar cell may be constructed by replacing the organic EL layer 26 with a known organic solar cell active layer. In the case of an organic solar cell in which the electrode foil of the present invention is used as an anode, the solar cell can be constructed by laminating, on a buffer layer (for instance, a carbon buffer layer), a hole transport layer (PEDOT:PSS (30 nm)), a p-type organic semiconductor layer (for instance, BP (benzoporphyrin)), an i-type mixing layer (for instance, BP:PCBNB (fullerene derivative) of an n-type organic semiconductor and a p-type organic semiconductor, an n-type organic semiconductor layer (for instance, PCBM (fullerene derivative)), a buffer layer having a low work function (for instance, Mg—Ag), and a transparent electrode layer (for instance, IZO) in this order. Known materials may be appropriately used for each of these layers without any particular limitation. The electrode used for organic solar cells may have the same materials and structure as an the electrode used for organic EL elements. The electrode foil of the present invention comprises a reflective layer and is thus expected to provide an increase in power generation efficiency due to light confinement caused by cavity effect.

FIG. 3 shows an example of a layer structure of a top-emission type organic EL lighting in which an organic EL element shown in FIG. 2 is incorporated. In the organic EL lighting shown in FIG. 3, the organic EL element is electrically connectable with a power source 30 through the metal foil 22 of the anodic electrode foil 20. On the buffer layer 25, the area that has no contact with the organic EL layer 26 is covered with an interlayer insulation film 29. The interlayer insulation film 29 is preferred to be a Si-based insulation film formed by CVD in that the film has a high barrier performance against water and oxygen that cause degradation of organic layers. A SiN-based insulation film is more preferable. A still more preferable interlayer insulation film is a SiNO-based insulation film in that the film has a small internal stress and an excellent bending performance.

On the upper side of the cathode 28, a sealing material 32 is provided as opposed to the organic EL element. The gap between the sealing material 32 and the organic EL element 20 is filled with a sealing resin to form a sealing film 34. As the sealing material 32, glass or films may be used. In the case of glass, the sealing material 32 may be bonded directly onto the sealing film 34 using a hydrophobic adhesive tape. In the case of films, both surfaces and end faces thereof may be covered with a Si-based insulating film. When a film having a high barrier performance will be developed in future, sealing will be possible without conducting coating treatment, and is expected to provide superior mass productivity. As the sealing material 32, films are preferable in terms of imparting flexibility. Nonetheless, a desired performance may be attained by using a sealing material formed by bonding a film to an extremely thin glass having a thickness of from 20 μm to 100 μm.

While various known cathodes used for top-emission type organic EL elements may be used as the cathode 28 without any particular limitation as long as they are transparent or translucent due to the necessity to transmit light, those having low work functions are preferred. Examples of preferable cathodes include conductive oxide films, magnesium alloy films, and fluoride films. A combination of two or more thereof is more preferable. For these films, films similar to those described with regard to the buffer layer of the electrode foil may be used.

A particularly preferable cathode has a two-layer structure in which a translucent metal layer as a buffer layer composed of a magnesium alloy film and/or a fluoride film is laminated onto a transparent oxide layer as a cathode layer composed of an conductive oxide film, being highly useful from the viewpoint of resistance as well. In this case, a high optical transparency and a low work function are provided by bringing the translucent metal layer (buffer layer) of the cathode 28 into contact with the organic EL layer 26, thereby enhancing brightness and power efficiency of the organic EL element. A most preferable example is a cathode structure formed by laminating a transparent oxide layer (cathode layer) composed of IZO (indium zinc oxide) and a translucent metal layer (buffer layer) composed of Mg—Ag. In addition, the cathode structure may have two or more transparent oxide layers and/or two or more translucent metal layers. Thus, the light generated in the organic EL layer 26 passes through the cathode 28, the sealing film 34, and the sealing material 32, and is then emitted outside.

On the back side of the electrode foil 20, an auxiliary substrate may be appropriately provided depending on type of usage. The portion does not affect light emission performance, so that materials may be selected with a high degree of freedom. For instance, a resin film such as polyethylene terephthalate (PET), polyimide (PI), polycarbonate (PC), polyethersulfone (PES), and polyethernitrile (PEN) may be optimally used because flexibility is not impaired.

FIG. 4 shows an example of a layer structure of a top-emission type organic EL element in which the electrode foil of the present invention is used as a cathode. The organic EL element shown in FIG. 4 comprises a cathodic electrode foil 40 comprising a metal foil 42, a diffusion prevention layer 43, a reflective layer 44 and a buffer layer 45; an organic EL layer 46 provided directly on the buffer layer 44; and an anode 48 as a counter electrode provided directly on the organic EL layer 46. The organic EL layer 46 may be composed similarly to the organic EL layer 26 shown in FIG. 2. The buffer layer 45 may be composed similarly to the cathode 28 shown in FIG. 2, and preferably composed of a conductive oxide film, a magnesium alloy film, a fluoride film, or a combination of two or more thereof. More preferably, the buffer layer 45 is a translucent metal layer composed of a magnesium alloy film and/or a fluoride film.

Specifically, the organic EL element that uses cathodic electrode foil 40 shown in FIG. 4 corresponds to a structure in which an organic EL element using the anodic electrode foil 20 shown in FIG. 2 is modified by exchanging the buffer layer 25 and the cathode 28 and reversing the lamination order from the anode side to the cathode side inside the organic EL layer 26. For instance, it is preferable that a magnesium alloy film or a fluoride film as the buffer layer 45 of the cathodic electrode foil 40 is formed by sputtering or vapor deposition while a film made of conductive amorphous carbon, MoO₃, or V₂O₅ is formed as the anode 48 by vapor deposition. In particular, in the case of forming a conductive amorphous carbon film on the organic EL layer, vacuum deposition is preferably used in order to avoid plasma damage during sputtering.

EXAMPLES

The present invention will be further described in detail with reference to the following examples. Although Examples 1 to 5 are categorized as reference examples as not directed to embodiments having a diffusion prevention layer, it is evident that the present invention achieves the given effects in light of the entire disclosure of the following examples and the common technical knowledge since the effect of preventing diffusion of metal by the diffusion prevention layers are demonstrated in Examples 6 to 8.

Example 1 Preparation of Cu/Al-alloy/ITO Electrode Foil

As a metal foil, 64 μm thick commercially available both-side-flat electrolytic copper foil (DFF (Dual Flat Foil), manufactured by Mitsui Mining & Smelting Co., Ltd.) was prepared. The surface roughness of the copper foil was measured with a scanning probe microscope (Nano Scope V, manufactured by Veeco Instrument Inc.) in accordance with JIS B0601-2001, resulting in an arithmetic average roughness Ra of 12.20 nm. This measurement was performed in an area of 10 μm square using a Tapping Mode AFM.

The copper foil was subjected to CMP (Chemical Mechanical Polishing) treatment with a polishing machine manufactured by MAT Inc. This CMP treatment was performed by using a polishing pad having XY grooves and a colloidal silica polishing liquid under the conditions of pad rotation speed of 30 rpm; load of 200 gf/cm²; and liquid supply rate of 100 cc/min. The copper foil thus treated with CMP was subjected to measurement of the surface roughness of the copper foil by using the scanning probe microscope (Nano Scope V, manufactured by Veeco Instruments Inc.) in accordance with JIS B 0601-2001, resulting in an arithmetic average roughness Ra of 0.7 nm. This measurement was performed in an area of 10 μm square using a Tapping Mode AFM. The thickness of the copper foil after the CMP treatment was 48 μm.

On the surface of the copper foil treated with CMP, an Al alloy reflective layer with a thickness of 150 nm was formed by sputtering. This sputtering was performed under the conditions of input power (DC) of 1,000 W (3.1 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flow rate of 100 sccm; and substrate temperature of room temperature, after mounting an aluminum alloy target (203.2 mm diameter and 8 mm thick) having a composition of Al-0.2B-3.2Ni (at %) in a magnetron sputtering apparatus (MSL-464, manufactured by Tokki Corp.) to which a cryopump was connected.

On the surface of an aluminum alloy reflective layer thus obtained, an ITO buffer layer with a thickness of 10 nm was formed by sputtering. This sputtering was performed under the conditions of input power (DC) of 300 W (0.9 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.35 Pa; Ar flow rate of 80 sccm; O₂ flow rate of 1.9 sccm; and substrate temperature at room temperature, after mounting an ITO (In₂O₃—SnO₂) target (203.2 mm diameter and 6 mm thick) containing 10 wt % of Sn in a magnetron sputtering apparatus (MSL-464, manufactured by Tokki Corp.) to which a cryopump was connected. Film thickness was controlled by regulating discharging time. The surface roughness of the buffer layer thus obtained was measured in the same manner as mentioned above, resulting in an arithmetic average roughness Ra of 2.0 nm. The total thickness of the resulting electrode foil was 48 μm.

Example 2 Preparation of Cu/Al-alloy/C Electrode Foil

An electrode foil was prepared in the same manner as in Example 1 except that a carbon buffer layer with a thickness of 1.7 nm or 3.5 nm was formed by sputtering in place of the ITO buffer layer. As a carbon target for the sputtering, two types of carbon targets were prepared including a non-treated carbon target with a purity of 3N (99.9%) made from a carbon material (IGS743, manufactured by Tokai Carbon Co., Ltd.); and a carbon target having a purity of 5N (99.999%) made from the above carbon material through purification treatment with a halogen gas. By using each of these targets, the carbon buffer layer was formed by sputtering. This sputtering was performed under the conditions of input power (DC) of 250 W (0.8 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flow rate of 100 sccm; and substrate temperature at room temperature, after mounting each carbon target (203.2 mm diameter and 8 mm thick) in a magnetron sputtering apparatus (Multi-chamber sheet-fed-type film formation apparatus MSL-464, manufactured by Tokki Corp.) to which a cryopump was connected. Film thickness was controlled by regulating discharging time. The surface roughness of the buffer layer thus obtained was measured in the same manner as in Example 1, resulting in an arithmetic average roughness Ra of 2.45 nm. The total thickness of the resulting electrode foil was 48 μm.

Example 3 Preparation of Cu/Ag-alloy/ITO Electrode Foil

An electrode foil having a buffer layer and a reflective layer was prepared in the same manner as in Example 1 except that an Ag alloy reflective layer with a thickness of 150 nm was formed by sputtering in place of the Al alloy reflective layer. This sputtering was performed under the conditions of input power (DC) of 150 W (1.9 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flow rate of 90 sccm; and substrate temperature at room temperature, after mounting a silver alloy target (101.6 mm diameter and 5 mm thick) having a composition of Ag-1.0Cu-1.0Pd (at %) on a magnetron sputtering apparatus (MSL-464, manufactured by Tokki Corp.) to which a cryopump was connected. Film thickness was controlled by regulating discharging time.

Example 4 Fabrication of Organic EL Element

An organic EL element having a structure as shown in FIGS. 2 and 3 except for the absence of a diffusion prevention layer was prepared by using as an anode the electrode foil (Cu/Al-alloy/ITO) prepared in Example 1. At the outset, a glass plate (3 cm square and 0.5 mm thick) was put on the electrode foil 20 (5 cm square) so as to make masking, followed by formation of an interlayer insulation film 29 composed of silicon nitride by plasma CVD (Chemical Vapor Deposition). This plasma CVD was performed under the conditions of film forming area of 8 inch diameter in terms of effective area; input power (RF) of 250 W (0.8 W/cm²); ultimate vacuum of lower than 5×10⁻³ Pa; sputtering pressure of 80 Pa; gas flow rate of SiH₄ (diluted with H₂ to 10%):NH₃:N₂=100:10:200 sccm; and substrate temperature at 250° C., using a plasma CVD apparatus (PD-2202L, manufactured by Samco Inc.) to which a mechanical booster pump (MBP) and a rotary pump (RP) were connected. The glass was then removed from the electrode foil 20 to obtain an interlayer insulation film 29 having an opening of 3 cm square on the electrode foil.

The surface of the electrode foil having the interlayer insulation film formed thereon was cleansed as follows. First, ultrasonic cleansing for 3 minute was performed twice in a bath filled with an ultrapure water (having larger than 18.0 MΩ) being replaced with a fresh one for the second cleansing. Subsequently, after water was removed by using nitrogen gas, after-curing was performed at 100° C. for 3 hours. The surface thus treated was cleansed by UV irradiation.

On the electrode foil thus cleansed, an organic EL layer 26, a cathode 28, a sealing layer 34, and a sealing material 32 were laminated. Specifically, on the buffer layer surface of the electrode foil, a 50-nm-thick hole injection layer composed of copper phthalocyanine, a 40-nm-thick hole transport layer composed of 4,4′-bis(N,N′-(3-tolyl)amino)-3,3′-dimethylbiphenyl (HMTPD), a 30-nm-thick light emitting layer composed of a host material doped with tris(2-phenylpyridine) iridium complex (Ir(ppy)₃), a 30-nm-thick electron transport layer composed of Alq3, a 10-nm-thick translucent layer composed of Mg—Ag (Mg:Ag=1:9), a 100-nm-thick transparent oxide layer composed of IZO (In—Zn—O), a 300-nm-thick passivation film (sealing layer) composed of silicon nitride, a 2,000-nm-thick adhesive layer, and a 200-μm-thick sealing glass (sealing material) were laminated in this order. The lamination of the sealing glass was conducted by using a double-stick tape, which corresponds to the adhesive layer. In this way, there was obtained an organic EL element sample as shown in FIG. 3, which was 50 mm square and 300 μm thick and had a light-emitting area of 30 mm square. When this sample was connected to a power source 30 and then applied with a voltage of 5.0 V, an intense light emission as shown in FIG. 5 was observed. In addition, when the applied voltage was varied to measure the change in brightness (cd/cm²) and current density (mA/cm²), there were obtained results shown in FIGS. 6 and 7 (see the plots denoted by “ITO” in these figures). As described above, the use of the electrode foil of the present invention enables light emission with an extremely high brightness at low voltages.

For comparison, when an organic EL element was prepared and applied with current in the same way as described above by using a both-side-flat electrolytic copper foil with an arithmetic average roughness Ra of 12.20 nm used in Example 1, short circuit occurred between the electrodes, failing to emit light.

Example 5 Fabrication of Organic EL Element

Three types of organic EL element samples were prepared in the same way as in Example 4 except for using electrode foils (Cu/Al-alloy/C) having the following three kinds of carbon buffer layers prepared in Example 2.

-   -   Sample “5N-C 35 Å” is an organic EL element having a         3.5-nm-thick carbon buffer layer formed by using a carbon target         having a purity of 5N,     -   Sample “3N-C 17 Å” is an organic EL element having a         1.7-nm-thick carbon buffer layer formed by using a carbon target         having a purity of 3N, and     -   Sample “5N-C 17 Å” is an organic EL element having a         1.7-nm-thick carbon buffer layer formed by using a carbon target         having a purity of 5N.

Each of the above samples was connected to the power source 30 as shown in FIG. 3. When the applied voltage was varied to measure the change in brightness (cd/cm²) and current density (mA/cm²), there were obtained results shown in FIGS. 6 to 8. As described above, the use of the electrode foil of the present invention enables light emission with an extremely high brightness at low voltages.

Example 6 Preparation and Heat-Resistance Evaluation of Cu/C/Al-alloy/C Electrode Foil

An electrode foil was prepared in the same manner as in Example 2 except that a carbon layer was formed by sputtering as a diffusion prevention layer between the copper foil and the Al-alloy reflective layer. This sputtering for forming the carbon diffusion prevention layer was performed, as in the formation of the carbon buffer layer in Example 2, under the conditions of input power (DC) of 250 W (0.8 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flow rate of 100 sccm; and substrate temperature at room temperature, after mounting a carbon target (203.2 mm diameter and 8 mm thick) having a purity of 5N (99.999%) in a magnetron sputtering apparatus (Multi-chamber sheet-fed-type film formation apparatus MSL-464, manufactured by Tokki Corp.) to which a cryopump was connected. Film thickness was controlled by regulating discharging time. Thus, the formation of the carbon diffusion prevention layer and the following formation of the Al-alloy reflective layer and the carbon buffer layer were performed by continuous film formation by means of sputtering.

The obtained Cu/C/Al-alloy/C electrode foil was subjected to heat treatment at 250° C. for 30 minutes under ambient atmosphere, in order to evaluate existence/absence of thermal migration. The laminate cross-section of the Cu/C/Al-alloy in the heat-treated electrode foil was observed by transmission electron microscope (TEM) to obtain a microphotograph shown in FIG. 9A. In addition, the thickness of the carbon diffusion prevention layer 63 was measured to be 1.7 nm. Energy dispersive X-ray analysis (EDX) was conducted on point B on the cross-section of the Al-alloy reflective layer 64 and on point C on the cross-section of the copper foil 62 in the laminate cross-section shown in FIG. 9A to obtain spectra to shown in FIGS. 9B and 9C, respectively. It can be understood from comparison between FIGS. 9B and 9C that Cu derived from the copper foil was not diffused into the Al-alloy reflective layer, in other words, diffusion of Cu into the Al-alloy reflective layer (thermal migration) was prevented by the carbon diffusion prevention layer.

Example 7 Preparation and Heat-Resistance Evaluation of Cu/Cr—Ti/Al-alloy/C Electrode Foil

An electrode foil was prepared in the same manner as in Example 2 except that a Cr—Ti layer was formed by sputtering as a diffusion prevention layer between the copper foil and the Al-alloy reflective layer. This sputtering for forming the Cr—Ti diffusion prevention layer was performed under the conditions of input power (DC) of 500 W (1.6 W/cm²); ultimate vacuum of lower than 5×10⁻⁵ Pa; sputtering pressure of 0.5 Pa; Ar flow rate of 100 sccm; and substrate temperature at room temperature, after mounting a Cr—Ti alloy target (203.2 mm diameter and 8 mm thick) having a composition of the weight ratio Cr:Ti=1:1 on a magnetron sputtering apparatus (Multi-chamber sheet-fed-type film formation apparatus MSL-464, manufactured by Tokki Corp.) to which a cryopump was connected. Film thickness was controlled by regulating discharging time. Thus, the formation of the Cr—Ti diffusion prevention layer and the following formation of the Al-alloy reflective layer and the carbon buffer layer were performed by continuous film formation by means of sputtering.

The obtained Cu/Cr—Ti/Al-alloy/C electrode foil was subjected to heat treatment at 250° C. for 30 minutes under ambient atmosphere, in order to evaluate existence/absence of thermal migration. The laminate cross-section of the Cu/Cr—Ti/Al-alloy in the heat-treated electrode foil was observed by transmission electron microscope (TEM) to obtain a microphotograph shown in FIG. 10A. In addition, the thickness of the Cr—Ti diffusion prevention layer 73 was measured to be 20 nm. Energy dispersive X-ray analysis (EDX) was conducted on point B on the cross-section of the Al-alloy reflective layer 74 and on point C on the cross-section of the copper foil 72 in the laminate cross-section shown in FIG. 10A to obtain spectra to shown in FIGS. 10B and 10C, respectively. It can be understood from comparison between FIGS. 10B and 10C that Cu derived from the copper foil was not diffused into the Al-alloy reflective layer, in other words, diffusion of Cu into the Al-alloy reflective layer (thermal migration) was prevented by the Cr—Ti diffusion prevention layer.

Example 8 Heat-Resistance Evaluation of Cu/Al-alloy/C Electrode Foil

For comparison, heat-resistance evaluation was performed on the Cu/Al-alloy/C electrode foil without diffusion prevention layer prepared in Example 2, in the same manner as in Examples 7 and 8. Specifically, the obtained Cu/Al-alloy/C electrode foil was subjected to heat treatment at 250° C. for 30 minutes under ambient atmosphere, in order to evaluate existence/absence of thermal migration. The laminate cross-section of the Cu/Al-alloy in the heat-treated electrode foil was observed by transmission electron microscope (TEM) to obtain a microphotograph shown in FIG. 11A. Energy dispersive X-ray analysis (EDX) was conducted on point B on the cross-section of the Al-alloy reflective layer 84 and on point C on the cross-section of the copper foil 82 in the laminate cross-section shown in FIG. 11A to obtain spectra to shown in FIGS. 11B and 11C, respectively. It can be understood from comparison between FIGS. 11B and 11C that Cu derived from the copper foil was diffused into the Al-alloy reflective layer to form a diffused layer with a thickness of about 100 nm, in other words, diffusion of Cu into the Al-alloy reflective layer (thermal migration) progressed in the absence of a diffusion prevention layer. 

The invention claimed is:
 1. An electrode foil comprising: a self-supporting metal foil having a thickness of 1 μm to 250 μm; a discrete diffusion prevention layer for preventing diffusion of metal derived from the self-supporting metal foil, the diffusion prevention layer being provided directly on the self-supporting metal foil; and a discrete reflective layer provided directly on the diffusion prevention layer; wherein an outermost surface on or to the side of the reflective layer is an ultra-smooth surface having an arithmetic average roughness Ra of 10.0 nm or less as measured in accordance with JIS B 0601-2001.
 2. The electrode foil according to claim 1 for use as an anode or a cathode in an organic EL element or an organic solar cell.
 3. The electrode foil according to claim 1, which is free from an insulating layer at least on or to the side of the reflective layer.
 4. The electrode foil according to claim 1, wherein the self-supporting metal foil is a nonmagnetic metal foil.
 5. The electrode foil according to claim 1, wherein the self-supporting metal foil is a copper foil.
 6. The electrode foil according to claim 1, wherein the diffusion prevention layer is a layer comprising at least one of Mo, Ti, Ta, Cr, W, Ni, Fe, Co, C, Zn, Li, Y, indium oxide, tin oxide, zinc oxide, molybdenum oxide, gallium oxide, vanadium oxide, tungsten oxide, ruthenium oxide, aluminum oxide, titanium oxide, titanium nitride, chromium nitride, tantalum nitride, NiP, Ni-Zn, LiF, MgF₂, CaF₃, NaAlF₆, and NaF₆.
 7. The electrode foil according to claim 1, wherein the reflective layer is at least one selected from the group consisting of an aluminum film, an aluminum alloy film, a silver film, and a silver alloy film.
 8. The electrode foil according to claim 1, further comprising a transparent or translucent buffer layer directly provided on the reflective layer, wherein the surface of the buffer layer constitutes the ultra-smooth surface.
 9. The electrode foil according to claim 8, wherein the buffer layer is at least one selected from the group consisting of an conductive amorphous carbon film, an conductive oxide film, a magnesium alloy film, and a fluoride film.
 10. The electrode foil according to claim 1, having a thickness of from 1 μm to 300 μm.
 11. The electrode foil according to claim 1, wherein a surface of the self-supporting metal foil opposite to the reflective layer is a roughened surface having a ten-point average roughness Rz of 1.0 μm or more as measured in accordance with JIS B 0601-1994.
 12. An organic device which is an organic EL element and/or an organic solar cell, the organic device comprising: the electrode foil according to claim 1; an organic semiconductor layer comprising an organic EL layer and/or an organic solar cell active layer, the organic semiconductor layer being provided directly on an outermost surface on or to the side of the reflective layer of the electrode foil; and a transparent or translucent counter electrode provided on the organic semiconductor layer.
 13. The organic device according to claim 12, wherein the counter electrode comprises at least one selected from the group consisting of an conductive amorphous carbon film, an conductive oxide film, a magnesium alloy film, and a fluoride film.
 14. An organic EL lighting comprising the organic device according to claim 12 as an organic EL element. 